Tetracyclines are one of the most well known antimicrobial agents. These are often prescribed against Gram-negative and Gram-positive organisms. The latest studies indicate that the resistance to tetracyclines is rising throughout the world. The aim of this study was to find out more about the reasons behind bacterial resistance to tetracycline. We performed a selective literature search by studying several articles which mentioned tetracyclines and their resistance mechanisms in various bacteria. We found that a rise in antibiotic resistance to tetracyclines is alarming. The most important mechanisms are ribosomal protection, efflux pumps, modification of the drug target and enzymatic alteration. The resistance mechanism to tigecycline is similar to the tetracycline; however, tigecycline remains partially intact from resistance.
This study was designed to survey the incidence of Enterococcus faecalis infection in symptomatic and asymptomatic root canals of necrotic teeth using PCR and to isolate the bacterium for further screening. Sixty patients categorized according to their clinical symptoms were used for sampling by insertion of paper points into the root canals and absorbing all the fluids present within them. The samples were incubated in 1.0 ml 2xYT (containing 16 g bacto tryptone, 10 g yeast extract and 5.0 g NaCl per liter) for 24 h at 37°C without aeration prior to multiplex PCR analysis. To assist the isolation of E. faecalis, subsamples were further grown in the same medium supplemented with 6.5% NaCl and back-inoculated into bile esculin. Using multiple cultivation-dependent and PCR analyses, 6 cases (10%) of E. faecalis were identified. Four isolates were obtained from asymptomatic cases of chronic apical periodontitis, and the other two were associated with phoenix abscess and acute apical abscess, respectively. No E. faecalis infection was found in 5 patients with acute apical periodontitis or in 9 with chronic suppurative periodontitis. Our results indicate that there is no significant difference in the incidence of E. faecalis between symptomatic and asymptomatic necrotic dental root canals (P > 0.05). (J. Oral Sci. 49, [221][222][223][224][225][226][227] 2007)
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